LOS ANGELES – On the match's first point, Serena Williams said she felt a twinge.

"It was in my stomach," she said. "I thought it was just a stitch."

She continued on. Ultimately, though, her injury, later diagnosed as a strained abdominal muscle, worsened to the degree that her serve became a poor, fluttering thing and Maria Sharapova was able to rally past her and claim the WTA Tour Championships 4-6, 6-2, 6-4.

Sharapova's victory before a Staples Center crowd of 11,397, the largest ever for women's tennis in Southern California, was her second over Williams, whom she also outplayed in this year's Wimbledon final.

The 17-year-old Sharapova thus reaped a $1 million reward in a match that was determined by a bellyache – the problem Williams experienced.

The strangest aspect of this odd encounter was that Williams had her greatest success when she apparently was experiencing the most discomfort. In the beginning of the the third set, she began swinging as forcefully as she could at every shot, everything was going in and she swept 16 of the set's first 18 points in assuming a 4-0 advantage.

"There was not too much I could do," said Sharapova. The teenager from Russia, however, did not lose her resolve and Williams' injury became increasingly limiting. Sixteen of the third set's final 20 points went to the winner.

Sharapova said she did not become aware her opponent was impaired until Williams called for a trainer with Sharapova holding a 5-2 advantage in the second set.

Williams left the court with the trainer but after about a 10-minute break returned and continued the match.

Her serve generally is Williams' strength; she can fire across deliveries caught at more than 120 mph. But her injury muffled her serve in the final phases of last night's match; she was pushing in serves as slow as 67 mph.

But in the players' rallies, Williams did not appear hampered.

"She didn't look as if she was injured," noted Sharapova. "I was just mentally strong. I knew if I could hold my serve, I could get a chance on her serve."

Of her injury, Williams said, "It's definitely a muscle strain or a tear, unfortunately."

Sharapova is the first Russian to capture this event. Williams captured this season-ending event in 2001.

By winning, Sharapova moved her ranking in the women's game from No. 6 to No. 4. Before this season, she had been ranked No. 32. In 2002, she was No. 186. Williams' ranking is to go from No. 8 to No. 7.

"I'm still in shock. I can't believe the way I pulled it out," said the Russian. "It's very unreal the way I stuck in there. It's been an amazing year."

Williams later said she did not know how she got through the match. She has a history of withdrawing when she is impaired, as she did last August after reaching the semifinals of the Acura Classic. She cited a knee injury. This time she persevered.

"I think I lived off her mistakes," Williams said of the run she made in the final set. "Once she stopped making them, she was able to come back and win the match. I don't know how I was able to stay out there. I can't imagine hitting a serve now."

For a time, before Williams' injury changed the nature of the match, the final had the look of a men's match, with Sharapova and Williams serving so forcefully that not much else could happen.